This invention relates to a variable capacity compressor for compressing refrigerant for use in air conditioning systems such as those for automotive vehicles, and more particularly to a compressor of this kind which has improved lubrication of its component parts.
Conventionally, a variable capacity compressor is known which is provided with capacity control means which is operable in response to discharge pressure thereof as control pressure. The known compressor has a first discharge pressure chamber disposed on one side of a pump body, in communication with a discharge port adapted to be connected to a refrigerating circuit, a second discharge pressure chamber disposed on another side of the pump body to be supplied with discharge pressure (control pressure), and a communication passage communicating the first and second discharge pressure chambers with each other. However, with such arrangement, pressure within the first pressure chamber and pressure within the second pressure chamber are different from each other so that there occurs a difference in oil surface level between oil sumps formed at lower portions of the respective discharge pressure chambers. Consequently, lubricating parts on the side of the oil sump having the lower oil surface level is lubricated to an insufficient extent.
More specifically, referring to FIGS. 1 and 2 showing the known variable capacity vane compressor, a cylinder is formed by a cam ring 1, and a front side block 2 and a rear side block 3 closing respective opposite ends of the cam ring 1. A front head 4 and a rear head 5 are secured to outer ends of the respective front and rear side blocks 2 and 3. A front discharge pressure chamber 6 and a rear discharge pressure chamber 7 are defined, respectively, between the front side block 2 and the front head 4, and between the rear side block 3 and the rear head 5. The discharge pressure chambers 6 and 7 communicate with each other via a communication passage 8, the front chamber 6 directly communicating with a discharge port 9 through which compression medium or refrigerant is discharged. A capacity control device 10 is provided in the rear side block 3 and operable in response to pressure within a suction chamber, not shown, as well as pressure within the rear discharge pressure chamber 7 to control the capacity of the compressor. The capacity control device 10 has a control pressure chamber 11, to which high discharge pressure within a discharge valve chamber 12 is supplied through first and second communication passages 13 and 14, the rear discharge pressure chamber 7, a third communication passage 15, in the mentioned order, for controlling the capacity of the compressor in cooperation with pressure within the suction chamber.
According to the known compressor, the rear discharge pressure chamber 7 is formed of a high pressure-introducing chamber section 7a located at an upper portion thereof, into which high discharge pressure is introduced from the discharge valve chamber 12, and an oil sump section 7b located at a lower portion thereof, the two sections 7a and 7b communicating with each other through a communication passage 7c defined in the rear head 5. With this arrangement, provided that the pressure within the discharge valve chamber 12 is designated by P.sub.d1, the pressure within the front discharge pressure chamber 6 P.sub.d2, and the pressure within the rear discharge pressure chamber 7 P.sub.d3, respectively, the relationship of P.sub.d1 &gt;P.sub.d2 &gt;P.sub.d3 holds, because the pressure P.sub.d2 acts as dynamic pressure, whereas the pressure P.sub.d3 acts as static pressure.
Consequently, the level L.sub.1 of the surface of oil stored in the rear oil sump section 7b is lowered to a level close to the communication passage 8 due to the pressure difference, while the level L.sub.2 of the surface of oil in the bottom of the front discharge pressure chamber 6 rises. As a result, an insufficient amount of oil can be supplied to lubricating parts on the rear side such as a rear bearing 17 supporting a drive shaft 16, resulting in poor lubrication of the rear side lubricating parts.